Re: "twins"

[aah@nofs.navy.mil]

>I meant as images upon a ccd frame possibly having different photocentre
>solutions due to marked brightness difference despite being same object,
>not resolved as (a) physical entity(ies) in Space.
  Then I don't follow your discussion.  Are you suggesting that
the astrometry has a systematic magnitude term, such that bright measures
would be at one position and faint measures would be at another?
Such is certainly possible with refractive optics, but might be difficult
to disentangle over a period of many nights for a CV since Tom's system won't
reposition the variable at the same point on the CCD.  You can search
for magnitude terms on a per-frame basis as I mentioned in response
to Patrick; that has much more potential for finding magnitude-related
distortions.
Arne